In recent years, MEMS (Micro Electro Mechanical Systems) devices are widely developed. The MEMS generally means a device technology such as an actuator and a sensor including micro mechanisms or a process technology developed on the basis of a semiconductor process for forming micro structures and mechanisms thereof. The MEMS device means an actuator or sensor manufactured using such an MEMS technology.
SOI (Silicon On Insulator) substrates are widely used for manufacturing MEMS devices. The SOI substrate is formed of a laminate of a supporting layer made from silicon, a BOX (Buried Oxide) layer made from silicon oxide (SiO2) formed on the supporting layer, and an active layer made from silicon bonded on the BOX layer. In structure design of the MEMS device manufactured from the SOI substrate, typically, structures and mechanisms serving as functional parts are formed in an active layer. Some of the structures are mechanically, electrically connected to the supporting layer via the BOX layer. Mechanical, electrical characteristics of the actuator or sensor serving as the MEMS device are formed in the active layer. The BOX layer and the supporting layer mainly serve to ensure rigidity and strength for packaging.
For example, Patent Literature 1 has disclosed a two-axis electrostatic tilt mirror element constituted of an SOI substrate.